I have 1988 d50 and my high beams won't turn on when I pull the switch. I have replaced the bulbs and still don't work.

Sounds to me like an electric issue. Did you check your fuses and fusable links? You got a test light or multimeter?

I checked the fuses and they are ok. But how do you check the fusable links I have a multimeter. Can it be a relay?

Fusable links are in a small black box near the brake booster. They are really easy to tell if they are broken. They get replaced but you make your own. Gotta buy a roll of the stuff and crimp spade connectors so they'll work. That is if they are broken.

Nope not the fuseable links they look fine I'll check the relay tomorrow cuz it's raining.

Is there 12v at the headlight with low beam as well as high beam? Are you sure it isn't the fuses? If it's not a fuse then it could be the switch or wiring harness. Glad you got a multimeter. Please update when you continue to diagnose.

Check the tension on the fuse socket for the high beam fuse and chek the back of the block for corrosion. After 22+ years the sides of the fuse holder gets weak and won't make good connection. windshield leaks are common right above the fuse block also.

Did you check to make sure the bulbs arent both out? I had that happen before. Otherwise for sure relay. Can't remmember where it is on the 2nd gen

is that where the water is coming from in my truck? I was ready to pull the carpet and make a few drain holes through frustration. Lol.